This invention relates to a method and apparatus for carrying out liquid chromatography, and more particularly to a method and apparatus for carrying out liquid chromatography which can effectively detect samples having a difficult electrolytic oxidation when an eluate solution from a separation column is electrochemically detected.
Liquid chromatography can be applied to analysis of a wide range of materials through a combination of various columns and detectors. However, an appropriate detector has not been available for detecting some kind of materials, for example, sulfur compounds, etc., and it is difficult to detect very small amounts of these materials.
Among the liquid chromatographic methods of detection, for example, an ultra-violet absorptiometric method generally has a high sensitivity, but is selective, and thus can be utilized only for the detection of materials having absorptions in an ultra-violet range. The ultra-violet absorptiometric method is not suitable for measurement of sulfur compounds. Other methods of detection, for example, a refractometric method or thermo-detective method, have a universal applicability, but a low sensitivity of detection. Furthermore, a radioactivity-detecting method has a high sensitivity, but cannot be universally applied owing to its restriction to handling.
Electrochemical detection methods, for example, polarography or coulometry, generally have a sensitivity as high as that of the ultra-violet absortiometric method, but are selective, and thus have no universal applicability. However, the methods can detect some of sulfur compounds such as H.sub.2 S, etc., though their sensitivity of detection is low, and thus are expected to have a possiblity to detect a very small amount of sulfur compounds.
In the conventional liquid chromatography provided with the electrochemical detector, it is impossible to detect sulfur compounds, for example, S.sup.2 .sup.-, HS.sup.-, SO.sub.3.sup.2 .sup.-, HSO.sub.3.sup.2 .sup.-, S.sub.2 O.sub.3.sup.2 .sup.-, S.sub.2 O.sub.6.sup.2 .sup.-, S.sub.4 O.sub.6.sup.2 .sup.-, etc. with a high sensitivity, because these sulfur compounds have a large overvoltage and their electrolytic oxidation is thus difficult to carry out.